For very many years, dental surgeons throughout the world have used a cartridge type of syringe to administer local anaesthetics. This type of syringe has a reusable actuating mechanism formed with a chamber into which is loaded a separate cartridge containing local anaesthetic agent—typically an amino-ester or an amino-amide mixed with a proportion of adrenaline. The cartridge has a slideable bung arranged to be engaged by a plunger of the actuating mechanism when the cartridge is in the chamber. After the cartridge has been loaded into the chamber a needle is attached to its forward end, usually by means of a screw thread arrangement. Then the practitioner can depress the plunger to drive the bung into the cartridge and expel the contents thereof to make an injection in the usual way. After use, the cartridge and needle are disassembled and disposed of, and the actuating mechanism sterilised for reuse.
A serious problem in this has emerged with the discovery that certain disease vectors—such as the prion proteins associated with variant Creutzfeldt Jakob disease (VCJD)—can survive conventional sterilisation. To counter this (and to provide certain other safety benefits) we have proposed the use of a wholly disposable syringe, in our international patent application PCT/GB01/02646, published as WO 01/95960.